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CS 5150 Software Engineering

Lecture 18

Security

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Topics for Next Presentation

Every project is different, but here are some suggestions:

General topics for every project

• A precise description of what you have agreed to deliver to your client (a shared definition of success).

• Summary of progress since last presentation.

• Test plan and test cases.

• Discussion of unexpected events and risks.

• Overview of plan to complete and deliver the project.

Topics that apply to many projects

• Results of user testing (if usability is important).  

• Technical issues (if you have a technical client).

A demonstration is always welcome

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Security in the Software Development Process

The security goal

The security goal is to make sure that the agents (people or external systems) who interact with a computer system, its data, and its resources, are those that the owner of the system would wish to have such interactions.

Security considerations need to be part of the entire software development process. They may have a major impact on the architecture chosen.

Example. Integration of Internet Explorer into Windows

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Agents and Components

A large system will have many agents and components:

• each is potentially unreliable and insecure

• components acquired from third parties may have unknown security problems

• commercial off-the-shelf (COTS) problem

The software development challenge:

• develop secure and reliable components

• protect whole system so that security problems in parts of it do not spread to the entire system

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Security Needs and Dangers

Needs

• Secrecy: control of who gets to read information• Integrity: control of how information changes or resources are used• Availability: providing prompt access to information and resources• Accountability: knowing who has had access to resources

Dangers

• Damage to information integrity• Disruption of service availability• Theft of money integrity• Theft of information secrecy• Loss of privacy secrecy

Butler W. Lampson, 2004

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Security Techniques: Barriers

Place barriers that separate parts of a complex system:

• Isolate components, e.g., do not connect a computer to a network

• Firewalls

• Require authentication to access certain systems or parts of systems

Every barrier imposes restrictions on permitted uses of the system

Barriers are most effective when the system can be divided into subsystems with simple boundaries

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Barriers: Firewall

Public network

Private network

Firewall

A firewall is a computer at the junction of two network segments that:

• Inspects every packet that attempts to cross the boundary

• Rejects any packet that does not satisfy certain criteria, e.g.,

an incoming request to open a TCP connectionan unknown packet type

Firewalls provide security at a loss of flexibility and a cost of system administration.

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Security Techniques: Authentication & Authorization

Authentication establishes the identity of an agent:

• What does the agent know (e.g., password)?

• What does the agent possess (e.g., smart card)?

• Where does the agent have physical access to (e.g., crt-alt-del)?

• What are the physical properties of the agent (e.g., fingerprint)?

Authorization establishes what an authenticated agent may do:

• Access control lists

• Group membership

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Example: An Access Model for Digital Content

Digital material

Attributes

Authentication

Role

Actions

OperationsAuthorization

Policies

User

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Security Techniques: Encryption

Allows data to be stored and transmitted securely, even when the bits are viewed by unauthorized agents and the algorithms are known.

• Private key and public key • Digital signatures

Encryption

Decryption

X Y

Y X

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Security and People

People are intrinsically insecure:

• Careless (e.g., leave computers logged on, leave passwords where others can read them)

• Dishonest (e.g., stealing from financial systems)

• Malicious (e.g., denial of service attack)

Many security problems come from inside the organization:

• In a large organization, there will be some disgruntled and dishonest employees

• Security relies on trusted individuals. What if they are dishonest ?

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Design for Security: People

• Make it easy for responsible people to use the system (e.g., make security procedures simple)

• Make it hard for dishonest or careless people (e.g., password management)

• Train people in responsible behavior

• Test the security of the system thoroughly and repeatedly, particularly after changes

• Do not hide violations

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Programming Secure Software

Programs that interface with the outside world (e.g., Web sites) need to be written in a manner that resists intrusion.

For the top 25 programming errors, see: Common Weakness Evaluation: A Community-Developed Dictionary of Software Weakness Types. http://cwe.mitre.org/top25/

• Insecure Interaction Between Components

• Risky Resource Management

• Porous Defenses

Project management must ensure that programs avoid these errors.

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Programming Secure Software

The following list is from the SANS Security Institute, Essential Skills for Secure Programmers Using Java/JavaEE, http://www.sans.org/

• Input Handling

• Authentication & Session Management

• Access Control (Authorization)

• Java Types & JVM Management

• Application Faults & Logging

• Encryption Services

• Concurrency and Threading

• Connection Patterns

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How Secure Should Your System Be?

"Practical security balances the cost of protection and the risk of loss, which is the cost of recovering from a loss times its probability... When the risk is less than the cost of recovering, it’s better to accept it as a cost of doing business ... than to pay for better security."

"Many companies have learned that although people may complain about inadequate security, they won’t spend much money, sacrifice many features, or put up with much inconvenience to improve it."

Butler W. Lampson, 2004

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Suggested Readings

Butler W. Lampson, Computer Security in the Real World. IEEE Computer, June 2004.

Trust in Cyberspace, Committee on Information Systems Trustworthiness, National Research Council (1999)http://www.nap.edu/readingroom/books/trust/ [Fred Schneider, Cornell Computer Science, was the chair of this study].